I. Field of the Invention
The present invention relates generally to the fields of echogenic biomedical devices. More particularly, it provides a brachytherapy device and method of manufacturing echogenic biomedical devices.
II. Description of Related Art
Ultrasonic imaging techniques have become increasingly prevalent in medical diagnosis and therapy over the last decades. The field includes needle biopsy positioning and the identification of medical abnormalities and fetal status in utero. To create echogenicity in an object or device one must provide a difference between the acoustic impedance of the object and the acoustic impedance of the surrounding medium. In the medical field, the surrounding medium is biological tissue or fluids such as blood, cerebral spinal fluid, or urine.
In the field of brachytherapy where radioactive sources are inserted into an organ or diseased tissue the precise placement is critical for calculated dose therapy in the organ or diseased tissue to insure appropriate dosage to the diseased tissue. The location of numerous radioactive sites must be carefully controlled to obtain the necessary radioactive dosing throughout the tumor or disease site. In brachytherapy of the prostate gland, source placement can be determined by ultrasonic imaging of the implant needles located within the gland. The procedure under a sterile field is simple, rapid, and effective provided the gland is implanted with sources in a predetermined array. Following implantation the proper placement must be determined by x-ray or magnetic resonance imaging since current brachytherapy sources are minimally echogenic if at all. If voids are identified a second procedure may be required or additional time may be required to reposition the patient. The field would be greatly improved if the brachytherapy sources were echogenic so as to provide real-time imaging of proper placement of the actual source during the procedure.
For almost two decades a plethora of approaches have been developed to enhance the echogenicity of medical devices by modifying the surface of the device. In U.S. Pat. No. 4,401,124 issued to Guess et al., the reflection coefficient of a biopsy needle is enhanced by means of a diffraction grating composed of groves diagonally machined into the needle tip. Elkins in U.S. Pat. No. 4,869,259 echogenically enhanced the needle by particle blasting with 50-micron particles to produce a uniformly roughened surface. In U.S. Pat. No. 4,977,897, Hurwitz machined sounding apertures into needles to match the incident beam wavelength this improving sonographic visibility. Bosley et al. (U.S. Pat. Nos. 5,081,997, 5,201,314 and 5,289,831) modified catheters and other devices by incorporating glass spheres or high-density metal particles in the range of 0.5 to 100 microns or partially spherical indentations. Rammler (U.S. Pat. No. 5,327,891) used micro-bubbles containing medium contained in vanes and/or tracks to echogenically enhance catheters. Davis et al. varied the configuration of the stylet inside the biopsy needle creating a series of annular groves about the stylet to enhance echogenicity of biopsy needles (U.S. Pat. Nos. 5,490,521, 5,820,554, and 6,018,676). In U.S. Pat. No. 5,759,154 Hoyns utilized a masking technique to produce depressions comprising alternating rows of squares and diamonds on the surface around the circumference of the device. Terwilliger modified the stylet by creating concave surfaces on the distal tip end in U.S. Pat. No. 5,766,135 and in U.S. Pat. No. 5,769,795 included a hole in the distal tip end to form a concave surface to reflect the ultrasonic beam. Each of U.S. Pat. Nos. 3,351,049, 6,099,458, 6,074,337, 4,994,013, 6,080,099, 4,702,228, 5,163,896, 6,132,677, 6,007,475, 5,976,067, 6,030,333, 6,059,714, 5,713,828, 6,132,359, 5,342,283, 6,099,457, 6,010,445, 6,059,714, 6,060,036, 6,146,322, and 6,159,142 disclosure devices with smooth surfaces that are not reflective from all angles. These smooth surfaces, like the smooth surface of a non-treated needle, create a surface that must be perfectly perpendicular to the ultrasonic emitter/receiver to result in an echogenic pattern.
Sarkis et al. in U.S. Pat. No. 5,921,933 claims echogenic enhancement by impregnating the echogenic portion with ultrasonically reflective particles. Violante et al. in U.S. Pat. No. 6,106,473 claimed an ultrasonically visible solid device in which the echogenic coating was applied to a solid matrix where the surface coating comprised bubbles of a non-gas material that changed phase to gas when heated.
However, each of these advancements in the filed of echogenic imaging contains limitations. In many, external modification of the surface is needed. This adds an additional and often expensive step to the manufacturing process. In other methods, the device modifications are such that the orientation of the device must be perfectly aligned with the ultrasonic emitter/receiver in order to be visible using echogenic imaging.
Another disadvantage of the current methods is the lack of means to consistently position implants without the use of additional processing. Current technology often requires the use of a several step process for placing radioactive sources into a tissue site including an imaging step after initial placement to determine where the radioactive sources were actually delivered in the tissue.
It would therefore be advantageous to have a device with enhanced echogenic properties without the need for an extra step in the formation of the device, the need for exacting positioning relative to the ultrasonic emitter/receiver during use, or the need for a separate imaging step during placement of radioactive sources.